This study was designed to test in cancer patients the immunomodulating effects of recombinant gamma interferon. Gamma interferon has some antitumor activity, but in in vitro systems and in animal models have been found to have significant immunomodulatory effects on macrophages. In this study, we wish to determine what effects the in vivo administration of gamma interferon has on monocyte function in humans. Varying doses of Gamma interferon were given to patients with malignant melanoma rendered disease free by surgery. Blood monocytes were collected before, during, and after the period of administration of gamma interferon and analyzed for expression of Fc receptors, HLADR, and hydroperoxide generation. The intent of the study was to try to determine the doses of gamma interferon that were required to bring about consistent immunologic alteration in these patients. Although of basic interest by itself, such immunologic alterations are also of potential importance when one wishes to combine gamma interferon with other agents such as tumor necrosis factor that are known to have syngernistic antitumor activity when used in combination both in vitro and in vivo in animal models. The results of this study will allow use to more intelligently choose doses of gamma interferon for use by itself and for use in combination with other biologicals.